Table 1.

Potential functions and parameters of united atom force field

Non-bond				Bond			Angle			Torsion
$$E_{\mathrm{nb}}=\left(\begin{array}{cc}\hfill 4ϵ\left[{\left(\frac{\sigma }{r}\right)}^{12}-{\left(\frac{\sigma }{r}\right)}^6\right]\hfill & \hfill ,r<r_c\hfill \\ \hfill 0\hfill & \hfill ,r\ge r_c\hfill \end{array}\right)$$				$$E_b=\frac{1}{2}{k}_{\mathrm{b}}{\left(r_b-r_0\right)}^2$$			$$E_{\mathrm{\theta }}=\frac{1}{2}{k}_{\mathrm{\theta }}{\left(\theta -{\theta }_0\right)}^2$$			$$E_{\mathrm{\varphi }}={\displaystyle \sum _{n=0}^3{A}_n{cos}^{n-1}}\left(\varphi \right)$$
	ϵ (kcal/mol)	σ (Å)	rc (Å)		kb (kcal/(mol·Å2))	r0 (Å)		kθ (kcal/mol)	θ0 (deg)		A0 (kcal/mol)	A1 (kcal/mol)	A2 (kcal/mol)	A3 (kcal/mol)
CHx… CHy (x = 1, 2, 3; y = 2, 3) [25]	0.1119	4.01	12	CHx-CHy	95.89	1.54	CHx-CH2-CHy	57.6	111.6	CHx-CH2-CH2-CHy	1.73	−4.493	0.776	6.99
				(x, y = 1, 2, 3) [27]
							(x, y = 1, 2, 3) [27]
										(x, y = 1, 2, 3) [25]
CH… CH [26]	0.0789	3.85	12				CHx-CH-CHy	62.1	109.74	CHx-CH-CH2-CHy	0.8143	1.7926	0.3891	3.6743
							(x, y = 2) [26]
										(x, y = 2) [28]